\documentclass[tikz]{standalone}

\begin{document}
\begin{tikzpicture}[scale=2]

  \draw[thick] (0,0) -- (0,3) -- (3,3) -- (3,0) -- cycle;

  \draw[<->, thick] (0,1.5) -- node[left]{$\frac{1}{3}a$} (1,1.5);
  \draw[<->, thick] (1.5,0) -- node[below]{$\frac{1}{3}a$} (1.5,1);
  \draw[<->, thick] (3,1.5) -- node[left]{$\frac{1}{3}a$} (2,1.5);
  \draw[<->, thick] (1.5,3) -- node[below]{$\frac{1}{3}a$} (1.5,2);

  \node at (1.5,-0.5) {Square with Midlines};
\end{tikzpicture}
\end{document}
